In association with the progress in the field of LSI toward larger scale and more sophisticated functions, the demands for a digital/analog hybrid circuit, in which a digital circuit and an analog circuit coexist in one piece of LSI, have been increasing. When simulating the digital/analog hybrid circuit as described above with a logic simulator, it is necessary to rewrite the digital/analog hybrid circuit to a circuit corresponding to characteristics of the logic simulator used for that purpose. Namely, it is necessary to rewrite the digital/analog hybrid circuit to a circuit for digital simulation in a case of a digital simulator, and to a circuit for analog simulation in a case of an analog simulator respectively.
FIG. 48 shows a digital/analog hybrid circuit (refer to Japanese Patent Laid-Open Publication No. HEI 4-71072) comprising a feedback loop for fetching an analog signal at a signal level in response to a 2-bit digital input value consisting of the output from an AND circuit 41 and that from a flip-flop (FF) 42 from a D/A converter (DAC) 43, inputting the analog signal via a circuit section comprising a resistor 44, an amplifier 44, resistors 46, 47, and a capacitor 48 to an A/D converter (ADC) 49, fetching a 2-bit digital output corresponding to an input signal level from the A/D converter (ADC) 49, outputting one bit thereof via an inverter 50 to the outside, and loading the other one bit thereof into the flip-flop (FF) 42.
In a case where the digital/analog hybrid circuit, in which a digital circuit portion and an analog circuit portion coexist as shown in FIG. 48, is simulated as it is with a digital simulator, the analog circuit portion comprising the D/A converter (DAC) 43, resistors 44, 46, 47, amplifier 45, capacitor 48, and A/D converter (ADC) 49 becomes a load to the simulation, and it becomes difficult to accurately simulate all functions within a short period of time. As a result, execution of high-speed simulation is impeded. This phenomenon is caused because the analog circuit portion comprises exponential information, which is different from simple binary information and is not suited to the processing for simulation. In other words, the reason is that bidirectionality of an analog element can not precisely be treated by the digital simulator.
As a result, if, for instance, data concerning a digital/analog hybrid circuit is inputted into a digital simulator, the analog circuit portion can not be verified and may be outputted as an error, which makes it difficult to execute high-speed simulation accurately. Especially, in a large-scale digital/analog hybrid circuit, the impedance as described above becomes considerable.
It should be noted that, also in a case where a logic gate circuit is subjected to circuit simulation at an analog transistor level with an analog simulator, efficiency is extremely low and the entire circuit can not be efficiently simulated.
For the reasons described above, conventionally high-speed simulation for a digital circuit portion and an analog circuit portion is efficiently realized by simulating the digital circuit portion with a dedicated digital simulator and also simulating the analog circuit portion with a dedicated analog simulator, respectively.
In a case of simulation with a digital simulator, it is necessary to rewrite a digital/analog hybrid circuit to a circuit for digital simulation.
For instance, in a case of the digital/analog hybrid circuit shown in FIG. 48, the digital circuit portion comprising the AND circuit 41, flip-flop (FF) 42, and inverter 20 must be rewritten to the circuit for digital simulation as shown in FIG. 49. Concretely, as shown in the figure, rewriting work is carried out to describe the D/A converter (DAC) 43 with a dummy circuit consisting of the AND circuits 51 and 52 and also to describe the A/D converter (ADC) 49 with a dummy circuit consisting of inverters 53 and 56.
It should be noted that the analog circuit portion comprising the D/C converter (DAC) 43, resistors 44, 46, 47, amplifier 45, capacitor 48, and A/D converter (ADC) 49 is rewritten to the circuit for analog simulation as shown in FIG. 50. Practically, however, the amplifier 45 is described with a circuit comprising transistors and resistors.
Also conventionally, in a case where a digital/analog hybrid circuit is simulated with a digital simulator as described above, all the work for rewriting the digital/analog hybrid circuit to a circuit for digital simulation has been carried out manually. In conventional technology, a scale of a digital/analog hybrid circuit itself is not so large, so that the work required for rewriting a digital/analog circuit to a circuit for digital simulation can be fully carried out manually, and in addition, the product development cycle is not so short. For this reason, the work can easily be carried out manually within a period of time allowance for a plurality of simulations until a required circuit is fixed.
In the conventional technology, in a case where a digital/analog hybrid circuit is simulated with a digital simulator, the digital/analog hybrid circuit is written to a circuit corresponding to characteristics of a logic simulator to be used completely through manual work, so that a large number of steps are required each time circuit conversion is to be executed.
The work for circuit conversion becomes more complicated as scale of a digital/analog hybrid circuitry becomes larger, and in manual work, such mistakes as transcription mistakes easily occur.
Further, at present, product development cycle is extremely short, while an extremely long period of time is required for circuit conversion work by executed simulation processing several times until a required circuit is fixed, if all the necessary work is executed manually.